A simple and sensitive spectrophotometric flow analysis method for determination of nitrate in waters with a wide range of salinities is presented. The use of a zinc column offers a promising means for reduction of nitrate to nitrite because of its simplicity, low cost, lack of toxicity, excellent reproducibility and high nitrate reduction efficiency. The proposed method may be used as an alternative to other FIA procedures involving the copperized cadmium column for the determination of nitrate in different water samples. This method allows the determination of nitrate with a detection limit of 1 μg L−1 which is comparable with or even better than some previously reported FIA methods using the Griess reagent (Table 1). The method has successfully been applied in extensive underway determinations of nitrate in estuarine and coastal marine waters.